After several millenia of wall construction using stone and mud as well as straw and clay and secret mixtures for mortar, modern masonry construction began with the development of portland cement just before the turn of the 20th century. The development of a mixture of sand, gravel, cement and water which could be poured, molded, and the like, and which would later set into solid form would not produce a useful construction material except for the fact that reinforcing steel can be used in the concrete to make reinforced concrete. Reinforced concrete is a composite material that is possible because the coefficients of expansion of steel and of stone are about the same. Steel alone is strong in tension but weak in compression, whereas concrete is strong in compression but weak in tension. When the two are used in combination the weaknesses cancel each other, producing a material which has the property of an instant rock that won't break or pull apart.
Concrete block was introduced to take advantage of the several functional attributes of clay brick, such as modular size, ease of manufacturing and handling, and still take advantage of the major advantage of concrete, the ability to be reinforced with steel. Concrete blocks are commonly made in hollow core units which are 8 inches high, 8 inches wide and 16 inches long, and are designed so that all of the hollow cores, or selected hollow cores, may be filled solid with concrete and reinforcing steel. The steel is normally placed both vertically and horizontally, and spans the length and depth of the multiple concrete block array.
Clay brick was also adapted for use in construction with reinforced concrete, with the new products being known as clay tile units. In many reinforced concrete wall applications the traditional clay brick continues to be used as an interior or an exterior "facing" material, primarily because of the decorative appeal of brick.
Even though concrete block and clay tile are used in modern structural construction only as a "remain in place" form for the reinforced concrete which is placed internally in the block, methods of wall erection have remained those traditionally used for a clay brick wall. That is, each modular unit is cemented into place using a mortar which weakly bonds that unit to adjacent units. This process is slow and labor-intensive, and requires a number of skills which may only be obtained through long apprenticeship or work experience. These factors have served to limit the widespread use of reinforced concrete in building construction. As a result, much effort has been spent since the introduction of concrete block as a building product in seeking a new method of constructing a concrete block wall which would not require additional masonry skills. The search for a new method of concrete wall erection has been primarily centered around one factor, the elimination of the need for a mortar bond between the blocks. With attention focused on the need to eliminate the mortar bond, most past attempts to develop a new method of concrete block wall erection have been directed toward new block design or toward improvements in block manufacturing equipment so as to manufacture a more precise concrete block unit.
The concrete block units are machine made, with a measured amount of concrete placed in a steel mold and compressed, usually by vibration, with the molded product removed for curing or firing before use as a building product. Because of the need for hollow core construction, which affects the geometry of the mold, and the difficulty of maintaining the exact volume of material introduced into the mold, concrete blocks are normally irregular in height. Although the variation between individual blocks is normally less than one-eigth of an inch, this irregularity is enough, because of the accumulation of errors, to prevent a true and plum wall from being laid up without the use of mortar.
A mason using mortar can make on-site corrections of irregularities in a concrete block wall as the wall is being built. The manner in which the irregularities are corrected is illustrated in FIG. 1, wherein the use of the mortarbed has eliminated the height irregularities in the concrete blocks, and any irregularities in the wall foundation. The mason will always work with a taut line and level to keep the tops of the concrete blocks of each new course level and true.
Attempts have been made to manufacture precision concrete blocks by making the blocks all slightly oversized and then running each block through a shaper, wherein a grinding process is utilized to obtain a uniform required height. The reverse method has also been tried, wherein all blocks were initially made undersized, and then a topping of cementitious material was applied to each block to build each block up to a uniform height.
A number of specially designed "dry-stack" blocks have been manufactured, with the most successful of these using a "precision" shoulder at the top of the block as an interlocking feature with the block stacked above. Such a block is illustrated in FIG. 2, and the rationale of the use of such a block design will be readily noted. The true block height "x" remains dimensionally unstable, but the dimension "y" is more precise since the shoulder on top of the block is machine made. A notable disadvantage of the use of these blocks lies in the potential for deformation of the base, since the uncured block can spread the "feet" which must support the entire weight of the block, unless extraordinary care is taken in block manufacture and handling.
The Bingham U.S. Pat No. 2,325,653 discloses a block or tile wall wherein facing strips of asphalted felt, impregnated cork, or a compound of asbestos fibers and asphalt are placed between the blocks of each course and between each of the courses in the wall. The strips are placed inward of the wall faces, so that when the blocks of the next course are set upon a given strip in proper relation to the course below a bonding space is provided longitudinally between the courses to receive bonding cement or mortar. The bonding cement or mortar is applied, with the spacers providing an effective seal along the bond areas against the passage of moisture through the wall, and prevent cement or mortar from dropping into the voids or aircells formed in the hollow tile or block. After the Bingham wall is constructed, the hollows in the blocks or tiles still remain, and no reinforcing steel is contemplated.
The Stevens U.S. Pat. No. 764,313 discloses the use of adhesive strips laid between and joining successive courses of building blocks. The adhesive strips may be of felt, paper, wood or any suitable absorbent material, which has been thoroughly impregnated with liquid cementing material such as asphalt. Stevens indicates that the strips when placed in position form positive supports for the blocks and compress equally. Thus the use of irregular blocks in the Stevens construction would result in the formation of a wall which was not true. The asphalt in the strips soon sets or hardens to form a joint of great strength and hardness which is much more durable than ordinary mortar. The joints between the adhered bricks can be pointed if desired. The blocks which are used in the Stevens patent do not appear to be hollow. Stevens teaches that a dead-air space may be left between the adhesive strips entirely around the block, or if desired the space may be filled with asphalt or other cementing material.
The Bennett U.S. Pat. No. 2,065,510 discloses the use of wood spacers having camming surfaces for leveling or positioning stones of irregular thickness.
Other patents relating to walls or the like of building blocks or tiles include Kertes U.S. Pat. No. 1,058,674, Sayers U.S. Pat. No. 1,785,499, Comm U.S. Pat. No. 3,722,168 and Klem U.S. Pat. No. 3,795,079.